Brain Responds Same to Acute And Chronic Sleep Loss

Brain Responds Same to Acute And Chronic Sleep Loss

The new study in rats adds to the growing evidence scientists are accumulating about the negative effects of restricted sleep for both the brain and the body. "There's a huge amount of interest in sleep restriction in the field today," says Doctor Chiara Cirelli, associate professor of psychiatry at the School of Medicine and Public Health, who led the research.

Many people are sleep restricted. "Instead of going to bed when they are tired, like they should, people watch TV and want to have an active social life," she says. "People count on catching up on their sleep on the weekends, but it may not be enough." This "casual" lack of sleep can be harmful.

"Even relatively mild sleep restriction for several nights can affect an individual's ability to perform cognitive tasks," Cirelli says. "For instance, recent studies in humans have shown that 5 days with only 4 h of sleep/night result in cumulative deficits in vigilance and cognition, and these deficits do not fully recover after one night of sleep, even if 10 hours in bed are allowed. Sleep restriction can also increase resistance to insulin, leading to a risk of diabetes."

Cirelli and her team kept rats awake 20 hours a day over five days while continuously recording the animals' brain waves. The EEGs measured slow wave activity (SWA), the best marker of an individual's need to sleep as well as the intensity of sleep that follows a period of wakefulness. "Slow-wave activity reflects the fact that sleep is regulated by homeostasis: in general, the longer we stay awake, the higher is SWA in the subsequent sleep. We knew that this was true after acute total sleep deprivation, now we found that this is also true after chronic sleep restriction. " Cirelli notes.

According to the rat cumulative SWA measures, the sleep restriction produced intense recovery sleep following each wake cycle, with both longer and deeper sleep. The more effective the researchers were in keeping the animals awake during those 20 hours, the larger the sleep rebound they saw during the following four hours.

Knowing that sleep restriction evokes the same brain response as sleep deprivation will help scientists better understand the harmful effects of sleep disturbances, says Cirelli.